(1) Field of the Invention
The present invention relates to the optical design of a reflector in the form of facets for reflecting light beams. Such reflectors are utilised, for example, for lighting for general illumination purposes. They have found wide application in fibre optics, for example. They are also utilised for light supply in video projectors or in spotlights which generate a sharply defined light field (so-called tracking spotlights).
(2) Description of Related Art
Such reflectors generally have an elliptical, parabolic or conical basic contour. In many cases an optical design in the form of facets is overlaid on this basic contour, in order to improve the uniformity of the light field and/or to increase the size of the light field.
In general, the aim is to have reflectors of this kind produce a circular light field. This is not always accomplished, however. The reason for this is that the illuminants being utilised are not rotationally symmetrical. The outcome of this is a light field which deviates from the circular form. It may be oval or similar to the shape of a right angle, which is undesired.
On the contrary, the case may arise where there was a light field deviating from the circular form, and where only rotationally symmetrical illuminants can be used only for manufacturing or installation reasons. With use of such a rotationally symmetrical illuminant a light field deviating from the circular form is therefore not possible with many means.
The object of the present invention is to develop an optical design for a reflector for reflecting light beams in such a way that light fields are created arbitrarily which are at least approximately circular or approximately rectangular, and this irrespective of the shape of the illuminant being used.
The inventors have acknowledged that a specific light field contour with a given form of the illuminant can be generated alone by choice of the forms of individual or all facets, as well as by arrangement or positioning of such facets relative to the optical axis of the reflector basic element.
The following problems are resolved by the present invention.
Either a non-rotationally symmetrical illuminant is presented the aim of which is to generate a round light field, or a rotationally symmetrical illuminant is presented the aim of which is to generate a non-circular light field. In both cases, the facets are formed and arranged such that rotational symmetry of the facets is substantially avoided, with respect to the optical axis of the basic reflector element.
The invention can be carried out in practice in a variety of ways.
With respect to the forms of the facets there are numerous possibilities. The facets can be flat, spherical or cylindrical. In the latter two cases they can also be concave or convex.
Deviation from the rotational symmetry may also be due to the fact that some groups of facets are larger and other groups are smaller. It is decisive that certain facets or groups of facets extending over a certain peripheral range of the basic reflector element differ from certain other facets or groups of facets with respect to their form and position, which extend over another peripheral range.
Known reflectors present facets which run in rows which in turn are arranged in planes vertical to the axis. In the plan view of the hollow basic reflector element, and therefore into this, the entire reflection surface can be divided into columns extending from the light outlet aperture of the reflector to mounting the illuminant. The dividing lines between adjacent columns can be coincident with meridian lines, but must not do so.
Likewise, the abovementioned rows must not run in planes vertical to the axis. They could also wind around the optical axis of the reflector in a spiral.
Of the countless ways of providing rotational asymmetry, the following possibility deserves mention: if the facets are of a cylindrical shape, the axes of the cylinders can run parallel to the optical axis of the reflector, though in a peripheral direction.
Another possibility consists of pairing uneven shapes with one another. An area of reflector inner surface can be formed from spherical facets, for example, while another area can be formed from flat facets. Another pairing between different columns can consist of concave and convex cylinders, or in large and small cylinders.